The present invention relates to a polarized-light illumination unit that illuminates a rectangular area uniformly using-polarized light whose polarization directions have been aligned. The present invention also relates to a projection-type image display unit that magnifies and projects images onto a screen by modulating polarized light emitted from the polarized-light illumination unit using a light valve.
Projection-type image display units using a liquid crystal panel as a light valve are excellent particularly in their small size, light weight, and ease of installation, and therefore have been forming a market rapidly as presentation tools. The projection-type image display units also are expected to become widespread in a consumer field, since they are excellent in their small size, light weight, and uniformity in image quality from the center to the periphery compared to a conventional CRT projection TV.
In the market of these projection-type image display units (hereafter referred to as xe2x80x9cliquid crystal projectorsxe2x80x9d) using a liquid crystal panel as a light valve, there are two needs, namely the increase in luminance and the reduction in cost.
With respect to the increase in luminance, it also is conceivable to handle it by replacing a light source with one that consumes a larger amount of electricity. However, this is a temporary countermeasure. Obviously, it is most desirable to handle it by further improving the utilization efficiency of light from the light source. A conventional liquid crystal light valve can utilize only one of two polarization directions, thus wasting half of the incident light as heat. However, based on the above-mentioned backgrounds, illumination units employing a system according to Publication of Japanese Unexamined Patent Application Tokkai Hei 8-304739 or a system to which said system is applied have been developed recently, thus improving the light utilization efficiency greatly. This configuration will be described with reference to FIG. 23 as follows.
A light source section 910 comprises a light-source lamp 911 and a reflector 912. Randomly polarized light emitted from the lamp 911 is reflected in one direction by the reflector 912 and enters a first lens plate 920 in an integrator optical system. The first lens plate 920 is a compound lens member in which many rectangular minute lenses 921 are arranged. The light that has entered there is gathered by respective minute lenses 921. Illuminant images are formed on a second lens plate 930 by the minute lenses 921. The second lens plate 930 comprises a condenser-lens array 931 that is placed in the vicinity of the position where the illuminant images are formed, a polarization-separation prism array 933 formed of an aggregate of polarization beam splitters 934, a xcex/2 phase-difference plate 935, and a lens 937 at the outgoing side. The illuminant images are formed on the array 931 by respective minute lenses 921 in the first lens plate 920. Then, a ray of light is separated by the polarization beam splitters 934 depending on its polarization direction. The polarization directions of the rays of light that have been separated are aligned by the xcex/2 phase-difference plate 935. After that, the rays of light pass through the lens 937 and illuminate an illumination area 940. Thus, the polarization directions of the randomly polarized light from the light-source lamp 911 can be aligned efficiently.
On the other hand, with respect to the reduction in cost, in order to reduce the cost of the liquid crystal panel, which has the highest proportion of cost in the entire costs, the effort for decreasing a panel size has been made. Concretely, the cost reduction is targeted by increasing the number of panels obtained at one time through changing panels with a diagonal length of 1.3 inches, which were the conventional majority, into those with a diagonal length of 0.9 inch and further into those with a diagonal length of 0.5 inch.
However, when seeking to maintain the same resolution as that in a conventional unit while decreasing panel size, damping of light increases in an effective image display area on a panel. Particularly, when a transmission light valve is used, apertures of pixels are decreased in size considerably, thus decreasing light transmittance.
As described above, the high luminance and the low costs have been very difficult to attain at the same time. Methods for tackling this include a method of improving an apparent numerical aperture by providing microlenses for respective pixels on a panel with a decreased size. In this method, however, the microlenses narrow down incident light once, but then a ray of light spreads. Therefore, an illumination unit that can provide light with a small spread angle, in other words, with a large illumination f-number, as incident light is required.
On the other hand, when actually manufacturing products using the method in the Publication of Japanese Unexamined Patent Application Tokkai Hei 8-304739, it is advantageous in practice to form the polarization beam splitters 934 using prisms with a parallelogramatic cross-sectional shape. Therefore, the prisms with this shape are mounted in current products. Further, in order to process the prisms at low cost, it is desirable that all the aforementioned polarization beam splitters 934 have the same thickness in the direction of the system optical axis 952 (a distance between two opposed planes orthogonal to the system optical axis). As a result, all the prisms forming the polarization beam splitters have the same shape. Consequently, when the shape of the prisms is designed to correspond to the biggest illuminant image in the vicinity of the central portion (in the vicinity of the system optical axis) in the illuminant images formed on the condenser lens array 931, the prisms have a useless portion for relatively small illuminant images formed at the periphery. Therefore, the second lens plate 930 itself is increased in size, and thus illumination light comes to have a small illumination f-number and a wide incidence angle, which has been a problem.
Thus, in the conventional technique, high luminance and the low costs have been difficult to attain at the same time.
The present invention seeks to solve the above-mentioned conventional problems. It is an object of the present invention to provide a polarized-light illumination unit in which illumination light spreads a little (the illumination f-number is large) and the polarization directions of randomly polarized light from a light source can be converted to a desired polarization direction.
It is another object of the present invention to provide a low-cost pojection-type image display unit that has high light utilization efficiency thus enables images with high luminance to be obtained.
In order to attain the above-mentioned objects, the present invention employs the following configurations.
A polarized-light illumination unit according to a first configuration of the present invention comprises: a light source for emitting randomly polarized light; an integrator optical system having a first lens plate formed of an aggregate of a plurality of rectangular lenses, a second lens plate formed of an aggregate of a plurality of minute lenses corresponding to the rectangular lenses one to one, and a condenser lens; a polarization separation section for separating the light emitted from the light source into two polarized lights whose polarization directions are orthogonal to each other and whose optical axes are substantially parallel to each other; and a polarization conversion section for aligning the polarization directions of the two polarized lights. The respective rectangular lenses are formed to have shifted centers of aperture and curvature so that illuminant images are formed in a plurality of rows on the second lens plate by the rectangular lenses in the first lens plate. The minute lenses in the second lens plate are arranged in a form of a plurality of rows at the positions where the illuminant images are formed by the rectangular lenses. The plurality of rows of the minute lenses includes at least one row with a different width H in a direction orthogonal to the longitudinal direction of the rows from that of the other rows. The polarization separation section is formed by assembling a plurality of minute polarization beam splitters. Each minute polarization beam splitter has a reflection-mirror plane provided obliquely to the system optical axis, a polarization separation plane provided in parallel to the reflection-mirror plane, and two planes orthogonal to the system optical axis. The polarization separation plane has a polarization separation film that separates light from the second lens plate by transmitting or reflecting the light depending on its polarization direction. All the minute polarization beam splitters forming the polarization separation section have the same distance d between the two planes orthogonal to the system optical axis. At least one minute polarization beam splitter with a different distance h between the reflection-mirror plane and the polarization separation plane from that of the other splitters is included.
A polarized-light illumination unit according to a second configuration of the present invention comprises: a light source for emitting randomly polarized light; an integrator optical system having a first lens plate formed of an aggregate of a plurality of rectangular lenses, a second lens plate formed of an aggregate of a plurality of minute lenses corresponding to the rectangular lenses one to one, and a condenser lens; a polarization separation section for separating the light emitted from the light source into two polarized lights whose polarization directions are orthogonal to each other and whose optical axes are substantially parallel to each other; and a polarization conversion section for aligning the polarization directions of the two polarized lights. The respective rectangular lenses are formed to have shifted centers of aperture and curvature so that illuminant images are formed in a plurality of rows on the second lens plate by the rectangular lenses in the first lens plate. The minute lenses in the second lens plate are arranged in a form of a plurality of rows at the positions where the illuminant images are formed by the rectangular lenses. The plurality of rows of the minute lenses includes at least one row with a different width H in a direction orthogonal to the longitudinal direction of the rows from that of the other rows. The polarization separation section is formed by assembling a plurality of minute polarization beam splitters. Each minute polarization beam splitter has a polarization separation plane provided obliquely to the system optical axis, a plane provided in parallel to the polarization separation plane, and two planes orthogonal to the system optical axis. The polarization separation plane has a polarization separation film that separates light from the second lens plate by transmitting or reflecting the light depending on its polarization direction. All the minute polarization beam splitters forming the polarization separation section have the same distance d between the two planes orthogonal to the system optical axis. At least-one minute polarization beam splitter with a different distance h between the polarization separation plane and the plane parallel thereto from that of the other splitters is included.
A polarized-light illumination unit according to a third configuration of the present invention comprises: a light source for emitting randomly polarized light; an integrator optical system having a first lens plate formed of an aggregate of a plurality of rectangular lenses, a second lens plate formed of an aggregate of a plurality of minute lenses corresponding to the rectangular lenses one to one, and a condenser lens; a polarization separation section for separating the light emitted from the light source into two polarized lights whose polarization directions are orthogonal to each other and whose optical axes are substantially parallel to each other; and a polarization conversion section for aligning the polarization directions of the two polarized lights. The respective rectangular lenses are formed to have shifted centers of aperture and curvature so that illuminant images are formed in a plurality of rows on the second lens plate by the rectangular lenses in the first lens plate. The minute lenses in the second lens plate are arranged in a form of a plurality of rows at the positions where the illuminant images are formed by the rectangular lenses. The plurality of rows of the minute lenses includes at least one row with a different width H in a direction orthogonal to the longitudinal direction of the rows from that of the other rows. The polarization separation section is formed by assembling a plurality of minute polarization beam splitters having the same shape. Each minute polarization beam splitter has a polarization separation plane provided obliquely to the system optical axis, a plane provided in parallel to the polarization separation plane, and two planes orthogonal to the system optical axis. The polarization separation plane has a polarization separation film that separates light from the second lens plate by transmitting or reflecting the light depending on its polarization direction.
A polarized-light illumination unit according to a fourth configuration of the present invention comprises: a light source for emitting randomly polarized light; an integrator optical system having a first lens plate formed of an aggregate of a plurality of rectangular lenses, a second lens plate formed of an aggregate of a plurality of minute lenses corresponding to the rectangular lenses one to one, and a condenser lens; a polarization separation section for separating the light emitted from the light source into two polarized lights whose polarization directions are orthogonal to each other and whose optical axes are substantially parallel to each other; and a polarization conversion section for aligning the polarization directions of the two polarized lights. The respective rectangular lenses are formed to have shifted centers of aperture and curvature so that illuminant images are formed in a plurality of rows or groups on the second lens plate by the rectangular lenses in the first lens plate. The minute lenses in the second lens plate are arranged in a plurality of rows or groups at the positions where the illuminant images are formed by the rectangular lenses. The plurality of rows or groups of the minute lenses have substantially the same width H in a direction orthogonal to their longitudinal direction. The polarization separation section is formed by assembling a plurality of minute polarization beam splitters having the same shape. Each minute polarization beam splitter has a polarization separation plane provided obliquely to the system optical axis, a plane provided in parallel to the polarization separation plane, and two planes orthogonal to the system optical axis. The polarization separation plane has a polarization separation film that separates light from the second lens plate by transmitting or reflecting the light depending on its polarization direction.
According to the polarized-light illumination units of the aforementioned first to fourth configurations, an illumination unit using an integrator optical system comprises a light source for emitting randomly polarized light, an integrator optical system including a second lens plate designed to have variant apertures, a polarization separation section for separating light into two polarized lights whose polarization directions are orthogonal to each other, and a polarization conversion section for aligning the polarization directions of the two polarized lights. Therefore, while the polarization directions of the randomly polarized light from the light source can be converted to a desired polarization direction, the spread of illumination light can be suppressed (the illumination f-number can be increased).
That is to say, since the polarized-light illumination units of the present invention can align the polarization directions of separated polarized lights in the same direction, when using one of them as an illumination unit that requires polarized light, particularly an illumination unit for a projection-type image display unit using a light valve for modulating light by utilizing polarization, the whole randomly polarized light from the light source can be utilized, thus improving the light utilization rate greatly. Further, polarization-separation devices can be formed corresponding to the sizes of illuminant images formed on the second lens plate by the first lens plate, and therefore the illumination f-number can be increased (the spread angle of incident light can be decreased). As a result, in the projection-type image display unit using one of the polarized-light illumination units of the present invention, picture images with high luminance can be obtained without changing the f-number of its projection optical system. In addition, when microlenses are formed on the incident surface of the light valve, the workload of the projection optical system decreases, thus easing obtaining the effect by the microlenses.
A projection-type image display unit according to the present invention comprises: a polarized-light illumination unit; a modulator having a light valve for displaying picture images corresponding to input signals by modulating polarized light from the polarized-light illumination unit; and a projection optical system that magnifies and projects modulated beams that have been modulated by the modulator. The projection-type image display unit is characterized in that the polarized-light illumination unit is any one of the aforementioned first to fourth polarized-light illumination units.
According to the projection-type image display unit of the above-mentioned configuration, since any one of the first to fourth polarized-light illumination units is used as an illumination unit for the projection-type image display unit using a liquid crystal light valve, polarized light whose planes of polarization are aligned can be supplied to a liquid crystal panel and therefore the light utilization efficiency increases, thus improving the brightness of projection image pictures. Since the polarizing plates absorb less heat, the temperature increase in the polarizing plates is suppressed. Further, a cooling system can be decreased in size and in noise. At the same time, a compact and low-cost unit can be obtained. In addition, since the illumination f-number can be increased, it is not necessary to design the projection lens to be particularly bright. As a result, the light utilization rate can be increased without increasing costs and size of the unit and decreasing contrast.